In conventional drum washing machines, a rotational speed of a drum is increased to a predetermined first value in determination of the weight of laundry in a drum and is further increased from the predetermined value to another second higher speed. The laundry weight is determined on the basis of the length of time length required for the rotational speed to be increased from the first value to the second value. However, when the rotational speed of the drum is in a higher range, windage loss occurs, or friction produced between an access cover of the drum in a stationary state and cloth is increased. As a result, it is difficult to obtain the detection results in proportional to the difference in laundry weight. Thus, the accuracy in the detection is reduced.
Furthermore, JP-6-275-A discloses a vector control controlling an output torque of an electric motor in a top loading type washing machine. A laundry weight is determined on the basis of a q-axis current value in the vector control. More specifically, since the q-axis current in the vector control is proportional to the output torque of the motor, the state of a load driven by the motor can be estimated properly by referring to the q-axis current value. Accordingly, the accuracy in the determination of laundry weight can be improved when the laundry weight is determined on the basis of the q-axis current value.
However, the technique disclosed by JP-6-275-A is applied to a top loading type washing machine in which an agitator mounted on the bottom of a wash tub is rotated. Thus, the disclosed technique cannot directly be applied to a drum washing machine. Furthermore, in order that an accurate laundry weight may be determined, it is ideal that laundry should be distributed uniformly in the drum so as to be well balanced. However, the above-noted publication discloses nothing in this respect, and further, the drum washing machine differs from the top loading type washing machine in the basic structure and accordingly, in the balancing system. As a result, the technique disclosed by JP-6-275-A cannot be applied directly to the drum washing machine.
Therefore, an object of the present invention is to provide a drum washing machine in which the laundry weight can be estimated with higher accuracy.